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the latter is an； inquiry into the cause of a given effect； and has
thus in it some semblance of an hypothesis （although； as I shall
show on another occasion； this is really not the fact）； it would
seem that； in the present instance； I had allowed myself to enounce
a mere opinion； and that the reader must therefore be at liberty to
hold a different opinion。 But I beg to remind him that； if my
subjective deduction does not produce in his mind the conviction of
its certitude at which I aimed； the objective deduction； with which
alone the present work is properly concerned； is in every respect
satisfactory。
As regards clearness； the reader has a right to demand； in the first
place； discursive or logical clearness； that is； on the basis of
conceptions； and； secondly； intuitive or aesthetic clearness； by means
of intuitions； that is； by examples or other modes of illustration
in concreto。 I have done what I could for the first kind of
intelligibility。 This was essential to my purpose； and it thus
became the accidental cause of my inability to do plete justice
to the second requirement。 I have been almost always at a loss； during
the progress of this work； how to settle this question。 Examples and
illustrations always appeared to me necessary； and； in the first
sketch of the Critique； naturally fell into their proper places。 But I
very soon became aware of the magnitude of my task； and the numerous
problems with which I should be engaged； and； as I perceived that this
critical investigation would； even if delivered in the driest
scholastic manner； be far from being brief； I found it unadvisable
to enlarge it still more with examples and explanations； which are
necessary only from a popular point of view。 I was induced to take
this course from the consideration also that the present work is not
intended for popular use； that those devoted to science do not require
such helps； although they are always acceptable； and that they would
have materially interfered with my present purpose。 Abbe Terrasson
remarks with great justice that； if we estimate the size of a work；
not from the number of its pages； but from the time which we require
to make ourselves master of it； it may be said of many a book that
it would be much shorter； if it were not so short。 On the other
hand； as regards the prehensibility of a system of speculative
cognition； connected under a single principle； we may say with equal
justice： many a book would have been much clearer； if it had not
been intended to be so very clear。 For explanations and examples；
and other helps to intelligibility； aid us in the prehension of
parts； but they distract the attention； dissipate the mental power
of the reader； and stand in the way of his forming a clear
conception of the whole； as he cannot attain soon enough to a survey
of the system； and the colouring and embellishments bestowed upon it
prevent his observing its articulation or organization… which is the
most important consideration with him； when he es to judge of its
unity and stability。
The reader must naturally have a strong inducement to co…operate
with the present author； if he has formed the intention of erecting
a plete and solid edifice of metaphysical science； according to the
plan now laid before him。 Metaphysics； as here represented； is the
only science which admits of pletion… and with little labour； if it
is united； in a short time； so that nothing will be left to future
generations except the task of illustrating and applying it
didactically。 For this science is nothing more than the inventory of
all that is given us by pure reason； systematically arranged。
Nothing can escape our notice； for what reason produces from itself
cannot lie concealed； but must be brought to the light by reason
itself； so soon as we have discovered the mon principle of the
ideas we seek。 The perfect unity of this kind of cognitions； which are
based upon pure conceptions； and uninfluenced by any empirical
element； or any peculiar intuition leading to determinate
experience； renders this pleteness not only practicable； but also
necessary。
Tecum habita； et noris quam sit tibi curta supellex。*
*Persius。 ＇Satirae iv。 52。 〃Dwell with yourself； and you will know
how short your household stuff is。〃
Such a system of pure speculative reason I hope to be able to
publish under the title of Metaphysic of Nature。 The content of this
work （which will not be half so long） will be very much richer than
that of the present Critique； which has to discover the sources of
this cognition and expose the conditions of its possibility； and at
the same time to clear and level a fit foundation for the scientific
edifice。 In the present work； I look for the patient hearing and the
impartiality of a judge； in the other； for the good…will and
assistance of a co…labourer。 For； however plete the list of
principles for this system may be in the Critique； the correctness
of the system requires that no deduced conceptions should be absent。
These cannot be presented a priori； but must be gradually
discovered； and； while the synthesis of conceptions has been fully
exhausted in the Critique； it is necessary that； in the proposed work；
the same should be the case with their analysis。 But this will be
rather an amusement than a labour。
PREFACE TO THE SECOND EDITION； 1787
Whether the treatment of that portion of our knowledge which lies
within the province of pure reason advances with that undeviating
certainty which characterizes the progress of science； we shall be
at no loss to determine。 If we find those who are engaged in
metaphysical pursuits； unable to e to an understanding as to the
method which they ought to follow； if we find them； after the most
elaborate preparations； invariably brought to a stand before the
goal is reached； and pelled to retrace their steps and strike
into fresh paths； we may then feel quite sure that they are far from
having attained to the certainty of scientific progress and may rather
be said to be merely groping about in the dark。 In these circumstances
we shall render an important service to reason if we succeed in simply
indicating the path along which it must travel； in order to arrive
at any results… even if it should be found necessary to abandon many
of those aims which； without reflection； have been proposed for its
attainment。
That logic has advanced in this sure course； even from the
earliest times； is apparent from the fact that； since Aristotle； it
has been unable to advance a step and； thus； to all appearance has
reached its pletion。 For； if some of the moderns have thought to
enlarge its domain by introducing psychological discussions on the
mental faculties； such as imagination and wit； metaphysical；
discussions on the origin of knowledge and the different kinds of
certitude； according to the difference of the objects （idealism；
scepticism； and so on）； or anthropological discussions on
prejudices； their causes and remedies： this attempt； on the part of
these authors； only shows their ignorance of the peculiar nature of
logical science。 We do not enlarge but disfigure the sciences when
we lose sight of their respective limits and allow them to run into
one another。 Now logic is enclosed within limits which admit of
perfectly clear definition； it is a science which has for its object
nothing but the exposition and proof of the formal laws of all
thought； whether it be a priori or empirical； whatever be its origin
or its object； and whatever the difficulties… natural or accidental…
which it encounters in the human mind。
The early success of logic must be attributed exclusively to the
narrowness of its field； in which abstraction may； or rather must；
be made of all the objects of cognition with their characteristic
distinctions； and in which the understanding has only to deal with
itself and with its own forms。 It is； obviously； a much more difficult
task for reason to strike into the sure path of science； where it
has to deal not simply with itself； but with objects external to
itself。 Hence； logic is properly only a propaedeutic… forms； as it
were； the vestibule of the sciences； and while it is necessary to
enable us to form a correct judgement with regard to the various
branches of knowledge； still the acquisition of real； substantive
knowledge is to be sought only in the sciences properly so called；
that is； in the objective sciences。
Now these sciences； if they can be termed rational at all； must
contain elements of a priori cognition； and this cognition may stand
in a twofold relation to its object。 Either it may have to determine
the conception of the object… which must be supplied extraneously；
or it may have to establish its reality。 The former is theoretical；
the latter practical； rational cognition。 In both； the pure or a
priori element must be treated first； and must be carefully
distinguished from that which is supplied from other sources。 Any
other method can only lead to irremediable confusion。
Mathematics and physics are the two theoretical sciences which
have to determine their objects a priori。 The former is purely a
priori； the latter is partially so； but is also dependent on other
sources of cognition。
In the earliest times of which history affords us any record；
mathematics had already entered on the sure course of science； among
that wonderful nation； the Greeks。 Still it is not to be supposed that
it was as easy for this science to strike into； or rather to construct
for itself； that royal road； as it was for logic； in which reason
has only to deal with itself。 On the contrary； I believe that it
must have remained long… chiefly among the Egyptians… in the stage
of blind groping after its true aims and destination； and that it
was revolutionized by the happy idea of one man； who struck out and
determined for all time the path which this science must follow； and
which admits of an indefinite advancement。 The history of this
intellectual revolution… much more important in its results than the
discovery of the passage round the celebrated Cape of Good Hope… and
of its author； has not been preserved。 But Diogenes Laertius； in
naming the supposed discoverer of some of the simplest elements of
geometrical demonstration… elements which； according to the ordinary
opinion； do not even require to be proved… makes it apparent that
the change introduced by the first indication of this new path； must
have seemed of the utmost importance to the mathematicians of that
age； and it has thus been secured against the chance of oblivion。 A
new light must have flashed on the mind of the first man （Thales； or
whatever may have been his name） who demonstrated the properties of
the isosceles triangle。 For he found that it was not sufficient to
meditate on the figure； as it lay before his eyes； or the conception
of it； as it existed in his mind； and thus endeavour to get at the
knowledge of its properties； but that it was necessary to produce
these properties； as it were； by a positive a priori construction； and
that； in order to arrive with certainty at a priori cognition； he must
not attribute to the object any other properties than those which
necessarily followed from that which he had himself； in accordance
with his conception； placed in the object。
A much longer period elapsed before physics entered on the highway
of science。 For it is only about a century and a half since the wise
Bacon gave a new direction to physical studies； or rather… as others
were already on the right track… imparted fresh vigour to the
pursuit of this new direction。 Here； too； as in the case of
mathematics； we find evidence of a rapid intellectual revolution。 In
the remarks which follow I shall confine myself to the empirical
side of natural science。
When Galilei experimented with balls of a definite weight on the
inclined plane； when Torricelli caused the air to sustain a weight
which he had calculated beforehand to be equal to that of a definite
column of water； or when Stahl； at a later period； converted metals
into lime； and reconverted lime into metal； by the addition and
subtraction of certain elements；* a light broke upon all natural
philo